In a so-called IC tag reading device, if another reading device is present near the IC tag reading device, since interference may occur between the both reading devices, or between the reading device that should not respond to a radio IC tag normally and the radio IC tag, there is a possibility that the radio IC tag cannot be read normally due to interference between radiated electric waves.
As one of necessary technologies for avoiding such inconvenience, loading a LBT (listen before talk) function on a reading device is essentially required (for example, Non-Patent Document 1). The LBT function is a method in which the reading device radiates an electric wave in a bandwidth (carrier sense bandwidth), after confirming that an electric wave having power being equal to or higher than a predetermined level (carrier sense level) is not radiated therein, for a predetermined time (carrier sense time), so as to avoid interference between reading devices and between radio stations.
Moreover, as another technology, there is transmission time control. In some transmission time control technologies, a continuous transmittable time that is a time allowing a reading device to radiate an electric wave for reading is limited to a predetermined time period, and transmission stop time is provided so that, upon passage of the continuous transmittable time, the unit radio channel can be yielded to another radio station (for example, Non-Patent Document 1).
Non-Patent Document 1: “Information and Communication Council Sub-Committee on Information and Communication Technologies Power-Saving Radio System Committee report (proposal)”, (online), (searched on Nov. 8, 2006), Internet <http://www.soumu.go.jp/s-news/2005/pdf/051005—2—2.pdf>